1. Field of the Invention
The present invention relates to a vehicle-surroundings monitoring apparatus for monitoring the surroundings of a traveling vehicle for, for example, a vehicle traveling in a nearby lane.
2. Description of Related Art
Optical vehicle distance detecting apparatuses which are used as a vehicle-surroundings monitoring apparatus using image sensors have been well known in, for example, Japanese Patent Laid-Open No. 63-38085 and Japanese Patent Laid-Open No. 63-46363. In any case, the apparatuses include a pair of horizontally spaced optical systems which comprise lenses 1, 2 disposed horizontally apart from each other at a reference distance L, image sensors 3, 4 disposed at the focal distance f of these lenses 1, 2, and a signal processing device 30 connected to the image sensors 3, 4, as shown in FIG. 7.
In the conventional vehicle-surroundings monitoring apparatuses, a signal processing device 30 serves to shift image signals from the image sensors 3, 4 to electrically overlap them one over the other to thereby determine a distance R up to an object 31 based on the principles of trigonometry using the following equation: EQU R=f.multidot.L/p
where p represents a deviation or an amount of shift p by which the above two image signals have the best match.
Japanese Patent Publication No.4-161810 discloses a distance measuring or detecting method in which a vehicle-surroundings monitoring apparatus sets a plurality of windows on a display screen at specified positions for an image signal in order to detect a distance up to an object captured by these windows based on the principles of trigonometry. However, the conventional vehicle surroundings monitoring apparatus having an optical vehicle distance detecting device described above may mistakenly identify a lane marker (lane-separating line) or guard rail entered into the windows as a vehicle traveling in a nearby lane when the apparatus is used for monitoring following vehicles or nearby vehicles travelling in the adjacent lanes.